I am really new and have not done any programming in a long time so this may seem like a dumb question but - When I do this step:
3. Now use RubyGems to install Rails. Still in the Terminal application, issue the following command.

tp> sudo gem install rails --include-dependencies

I get a return statement - sudo: gem: command not found

Any suggestions about what is happening. I am showing a ruby version 1.8.2